Diffuse optical imaging (DOI) is a non-invasive and inexpensive imaging technique that uses near-infrared light (NIR) to probe tissue optical properties. In its most common application, DOI can measure regional changes in the concentration of oxy- and deoxy-hemoglobin with excellent sampling rates (exceeding 100 Hz, given suitable hardware). In diffuse optical topography (DOT), numerous light sources and detectors are employed, resulting in spatial maps of oxy- and deoxy-hemoglobin concentration changes. To date, there have been numerous demonstrations in adults that modulations of diffuse optical imaging signals elicited by perceptual and cognitive tasks can be detected non-invasively at the scalp. Yet, there has not been a systematic validation of DOT with more established techniques, leaving unresolved the issue of the true potential and limitations of DOT as a cognitive neuroscience tool. The general goals of the proposed research are to conduct such a systematic validation in adults by recording simultaneously DOT and fMRI data during established visual stimulation paradigms. The critical importance of conducting such a validation becomes apparent if one considers some of the potential benefits of DOT as a cognitive neuroscience tool: (1) DOT can be used safely with pediatric populations of any age; this is especially important for healthy infants and young children, in which fMRI cannot easily be used without extreme physical restraint measures (e.g., sedation); (2) The DOT equipment is portable and so can be used in settings where fMRI cannot (e.g., realistic settings such as driving a vehicle); (3) DOT monitors brain activation in a less intrusive manner than fMRI since acquisition is silent and subjects are only minimally constrained physically; (4) DOT is over an order of magnitude less expensive than fMRI; and (5) DOT can measure physiological parameters that are complementary to those measured by fMRI. Thus, the development and validation of DOT for the noninvasive study of brain function may result in an additional technique available to cognitive neuroscientists to investigate brain function and dysfunction in adults and especially in pediatric populations.